A team of researchers at the University of Strathclyde has developed a highly accurate way to assemble multiple micron-scale optical devices extremely close together on a single chip. According to the team, the approach could eventually support the ability of manufacturers to develop chip-based optical systems that enable more compact optical communications devices and advanced imagers at high volume. “The development of electronics that are based on silicon transistors has enabled increasingly more powerful and flexible systems on a chip,” said Dimitars Jevtics, from the University of Strathclyde. However, optical systems on a chip require the integration of different materials on a single chip — an obstacle that has prevented the design of these nanoscale optical device components at the same scale as silicon electronics. Jevtics and his colleagues used a transfer printing process in the work, which Jevtics said could be upscaled in future work. “On-chip optical communications, for example, will require the assembly of optical sources, channels, and detectors onto subassemblies that can be integrated with silicon chips,” Jevtics said. “Our transfer printing process could be scaled up to integrate thousands of devices made from different materials onto a single wafer. This would enable micron-scale optical devices to be incorporated into future computer chips for high-density communications or into lab-on-a-chip biosensing platforms.” Before transfer printing materials, the team developed a method to assemble multiple devices on a single chip that allowed it to place the multiple devices very close together without affecting the devices already present on the chip. Researchers at the University of Strathclyde developed a way assemble multiple nanoscale optical devices extremely close together on a single chip. They team's transfer printing method, part of the introduced technique, involved placing nanotubes 1 to 3 µm apart. The same group used the printing method to create semiconductor nanowire lasers. Courtesy of Dimitars Jevtics, University of Strathclyde. The group based this method on reversible adhesion, in which a device is picked up and released from its growth substrate and placed onto another surface. It used a soft polymer stamp mounted on a robotic motion control stage to pick up an optical device from the substrate on which it was made. The substrate onto which it was placed was then positioned under the suspended device and accurately aligned using a microscope. Once aligned properly, the researchers brought the two surfaces into contact, which released the device from the polymer stamp and deposited it onto the target surface. “By carefully designing the geometry of the stamp to match the device and controlling the stickiness of the polymer material, we can engineer whether a device will be picked up or released,” Jevtics said. “When optimized, this process does not induce any damage and can be scaled up using automation to be compatible with wafer-scale manufacturing.” The researchers successfully integrated aluminum gallium arsenide, diamond, and gallium nitride optical resonators onto a single chip. These optical resonators exhibited strong optical transmission, which the researchers said demonstrated that the integration worked well. They also used the printing approach to create semiconductor nanowire lasers. The researchers placed nanowires onto host surfaces in spatially dense arrangements, where measurements of the separation between the nanowires demonstrated a spatial accuracy in the 100-nm range. They also placed semiconductor nanowires on silicon dioxide to create a multiwavelength nanolaser system. “As a manufacturing technique, this printing approach is not limited to optical devices,” Jevtics said. “We hope that electronics specialists will also see possibilities for how it could be applied in future systems.” The researchers aim to replicate these results with larger numbers of devices to show that it works at larger scales. They also want to combine their transfer printing approach with an automated alignment technique they developed previously to enable rapid measurement, selection, and transfer of hundreds of isolated devices for applications in imaging and hybrid optical circuits. This work was funded by the Engineering and Physical Sciences Research Council, the European Commission, and the Royal Academy of Engineering under the Research Chairs and Senior Research Fellowships scheme. The research was published in Optical Materials Express (www.doi.org/10.1364/OME.432751).